I know that my wife and I are completely comfortable with the idea of our 5 and 2 year old kids (when they were that old not long after we moved in) playing in our backyard whenever they want and we are still able to get some chores done (or whatever) inside the house - ie, we don't have to sit outside in the backyard with them the whole time to monitor them. They are safely contained in our backyard that we have ensured is safe for them.
Even if you live right next door to the park, unless your kids are at an age where it's OK for them to go down the street by themselves (ie head off out of sight and contact), I know there's no way either my wife and I would be able to let our kids play at the park without us going there with them.
If you say that you don't need a backyard because there's a park only a couple of doors down, I say that you are either willing to stop whatever you're doing and head to the park with your kids every time they ask or your kids will not get anywhere near as much time playing outside as they want.
My kids can go out and play in the backyard whenever they want and there's heaps of room out there for them to run around, ride their bikes, play ball games, plus their trampoline, swing set and cubby house. That's what our backyard is for. That's why we bought a block that was big enough that we'd have a large backyard.
Need I say more?
Completely agree with you Rodda
That was exactly my response to my friend.
My kids, especially my daughter, have been waiting for the house to be built because of the big backyard (and her own room, of course!)
I remember when we were visiting display houses for a year or so... she was always looking forward to see the backyard (though most display homes don't have big backyards). She made us promise to buy them a trampoline and a cubby house ... and waitiing for the time when we can ride our bikes to the park, which is a few steps away from us (that would be every weekend though.. hehe).